1. Field of the Invention
The present invention relates to rigid polyurethane foams, and more particularly, to rigid polyurethane foams prepared from polyvinyl acetate/allyl alcohol polyols and the process for making the same.
2. Description of Related Art
It is well known that a polyurethane foam having insulating utility can be prepared by reacting an organic polyfunctional isocyanate with a suitable hydroxyl component in the presence of a blowing agent such as a fluorinated hydrocarbon. The fluorinated hydrocarbons produce a desirable rise in the foamed product, but also play an important role in producing a foam having a low thermal conductivity or K factor. However, the use of fluorinated hydrocarbons adversely impacts the environment. Regulatory agencies have mandated a reduction in fluorinated hydrocarbon use and have called for the eventual elimination of the use of fluorinated hydrocarbons. Attempts have been made to substitute various blowing agents, such as water, in an effort to find a replacement for fluorinated hydrocarbons. Most of these attempts have produced unsatisfactory results. For instance, while water may be substituted for fluorinated hydrocarbons as a blowing agent, the CO.sub.2 produced by the water decreases the insulating properties of rigid foams. Heretofore, it has been known that use of copolymers in urethane systems could produce improved physical and chemical properties such as increased load supporting capacity, increased tensile strength, increased modulus of tensile elasticity, and increased solvent resistance. However, the use of a copolymer, particularly the copolymer used in the instant invention, to improve the resistance to thermal conductivity of the foam has not been recognized.